The present invention relates to an information transmission apparatus for encrypting a content and its additional information and transmitting a result of encryption, relates to an information reception apparatus for receiving as well as decrypting an encrypted content and its encrypted additional information and relates to an information-providing system including the information transmission apparatus and the information reception apparatus.
In recent years, there has been started the implementation of a service for providing a content by way of communication means such as the Internet. In order to prevent a content from being copied a limitless number of times in such a content-providing service, an indispensable copyright management technology must be adopted. As a copyright management technology, a content encryption technology is considered to be a technology widely used and indispensable.
A large number of contents include various kinds of additional information besides the main content. In the case of a musical content, for example, the main content is musical data itself whereas the additional information is a jacket picture, lyrics and other data. For details, for example, refer to Japanese Patent Laid-open No. 2003-84903. Many pieces of such additional information require copyright management as is the case with the main content. In such a case, it is thus desirable to encrypt additional information in the same way as the main content.
In this case, an encryption key having a length determined in advance in accordance with an encryption algorithm is used in a process to encrypt a content. If a main content and its additional information are encrypted by using the same encryption key, however, a plurality of pieces of data is encrypted by using the same encryption key and, in consequence, the encryption key can be inferred with ease from data obtained as a result of the encryption process. Thus, the danger of having the encryption key exposed to unauthorized persons is greater.
If an encryption key used for encrypting a main content is completely different from a key for its additional information, on the other hand, the danger of having the encryption key exposed to unauthorized persons is smaller. In this case, however, the following problem is raised.
A plurality of encryption keys must be described in a package or a file used as a file for containing information on keys. Thus, the length of data rises by an increase proportional to the number of encryption keys. This increased length of data raises a problem particularly in a consumer electronic apparatus, which has a memory with a small storage capacity.
In addition, it is necessary to protect a file used as a file for containing information on keys by using a safe method. In the creation of the file, a large number of processes is thus involved. If the amount of additional information needs to be changed, however, it is necessary to recreate a file used as a file for containing information on keys. As a result, a big loss is incurred.
Furthermore, an encryption key itself is information that must be protected safely. Thus, if a number of encryption keys exists for a content, the cost for managing the keys is high.